1. The Field of the Invention
This invention relates to mechanical sorters and separators and, more particularly, to a novel apparatus and method for separating good raisins from moldy raisins.
2. The Prior Art
Various kinds of dried fruits are quite popular both as snack foods and as cooking ingredients. One of the most widely used dried fruits is the raisin, which is a dried, ripe, sweet grape. Raisins are presently used in a seemingly limitless variety of products, including commercial cereals and a large assortment of baked goods; and raisin growers, which are located in various parts of the country, invest substantial resources to provide the needed raisin supply.
In order to produce raisins, a raisin grower first raises sweet grapes until they are ripe. At such time, paper is generally spread on the ground between the rows of grapes; and the ripened grapes are thereafter picked and placed on the paper where they are allowed to dry in the sun. It usually takes several weeks for the grapes to dry properly; and, during this time, the grapes must be turned over regularly in order to prevent spoilage. Finally, after the grapes are properly dried, the raisins ae sorted and shipped to a packaging facility.
One of the major difficulties encountered by raisin growers is crop spoilage due to mold. Since, as described above, the raisins are typically dried in the sun, any precipitation or excessive humidity during the drying period significantly increases the risk that some of the raisins will become moldy. In fact, even if mechanical drying devices are used, the possibility of mold development still exists. It will be readily appreciated that if significant portions of the raisin crop become moldy, the crop will be significantly reduced in value.
In order to help minimize the effects of such raisin spoilage, those skilled in the art of raisin production have developed various devices and methods to separate good raisins from moldy raisins. Typically when using the prior art devices, the raisins are first treated in warm water and/or a peroxide solution. This treatment softens and partially decomposes the skin of each raisin. Importantly, since the moldy raisins decompose at a much faster rate than the good raisins, the moldy raisins quickly become very soft and sticky. In fact, as a result of the treatment, it is not uncommon for the moldy raisins to substantially decompose to the point where they become white and "musky." Although the good raisins are also somewhat decomposed, the good raisins, on the other hand, tend to maintain a relatively tough outer skin.
Following this preliminary treatment, the raisins are then placed into a separator device. Various different kinds of separator devices are currently in use, and these devices may be used either alone or in combination with each other.
One of the most common types of prior art device comprises a large bin, having screens at the sides and at the bottom thereof, and a large auger, which is rotated within the bin adjacent the screens. Because of their soft, mushy texture, the moldy raisins tend to stick to the screens at the sides and at the bottom of the bin. Thus, as the auger rotates, the moldy raisins are squashed through the screens and are thereafter collected and disposed of as feed or mesh. Often the bin of this device also serves to hold the water or peroxide which is used for treating the raisins prior to separation. Accordingly, the bin is often equipped with one or more large heating elements.
A second type of prior art device which is sometimes used together with the device described above comprises a laterally inclined conveyor belt which is rapidly agitated by a shaker mechanism. The pretreated mixture of good and moldy raisins is deposited onto one end of the belt. Then, as the belt is agitated, the good raisins are bounced down the belt and are collected at the bottom thereof. The moldy raisins, on the other hand, tend to stick to the belt, and they are thus carried to the top end of the belt where they are removed by a suitable water jet or scraper. Frequently, in order to increase the effectiveness of the device, this device includes a plurality of such belts which are arranged in parallel fashion.
A third type of prior art device comprises an inclined, rotating cylindrical screen. The rotating cylinder causes the raisins to be successively lifted and dropped as the raisins travel from one end of the cylinder to the other. The good raisins tumble freely toward the bottom end of the cylinder and are collected. The moldy raisins, however, stick to the sides of the cylinder and are thereafter washed into a collecting trough.
A fourth type of prior art device comprises two cylinders, each of which has a plurality of blunt rods affixed to the surface thereof. Importantly, the rods are staggered such that the rods on one cylinder mesh with the rods on the other cylinder, and the two cylinders are simultaneously rotated in opposite directions. The hydrogen peroxide treated mixture of good and moldy raisins is deposited between the two rotating cylinders such that each raisin is individually pressed by one of the rods. As a result, the moldy raisins stick to the rods and are thereafter scraped into a suitable container. The good raisins, however, do not stick to the rods but drop downward into a separate collecting bin.
Although the prior art type devices have been somewhat successful in minimizing the effects of raisin spoilage due to mold, these devices have been found to be inadequate in several respects. First, it is quite expensive to separate raisins using the prior art devices. For example, a substantial amount of energy may be required to heat the water which is used to pretreat the raisins. Similarly, considerable energy may be required to drive the large rotating augers or cylindrical screens of the prior art separator devices. In addition, since the raisins are pretreated in a solution of hydrogen peroxide, it is usually necessary to redry the good raisins after the separation process. Although such redrying is often done mechanically, it may be both time consuming and costly.
It has also been found that the prior art devices are not sufficiently effective in separating the raisins. For example, when using a separator which has rotating cylinders it is necessary to press each raisin twice, once from each side, in order to effect satisfactory separation. Also, as noted above, raisin growers often use two or more of the prior art devices together, in order to increase their effectiveness in accomplishing the desired separation of moldy raisins.
One of the most significant drawbacks of the prior art type devices is that many of the raisins are damaged during the separation process. As mentioned above, the pretreatment of the raisins accelerates the decomposition of both the good and the moldy raisins. As a result, many of the moldy raisins are reduced to a mere paste, and a substantial number of the good raisins are also affected. It will be readily appreciated that even a partial decomposition of the good raisins results in an overall lower quality raisin crop.
In addition to the damage caused by pretreatment, the vigorous action of the various prior art devices may further damage the raisins. For example, the squashing action of the rotating auger-type device may damage many good raisins along with the moldy raisins. Likewise, the dropping or bouncing action of the inclined belt and screen cylinder-type devices is also damaging; and the pressing action of the rods of the rotating cylinder-type device may crush and destroy many of the raisins. Consequently, using the prior art devices, most of the moldy raisins are only good for feed or mash. Moreover, the good raisins may not be suitable for all uses and may thus demand a much lower price.
Accordingly, it would be an improvement in the art to provide an apparatus for separating good raisins from moldy raisins which does not require pretreatment of the raisins to accelerate their decomposition. It would also be an improvement in the art to provide an apparatus and method for separating raisins which is energy efficient and which does not require that the raisins be redried following separation. Additionally, it would be an improvement in the art to provide an apparatus for separating good raisins from moldy raisins which effectively separates the raisins in a single treatment. Further, it would be an improvement in the art to provide an apparatus and method for separating raisins which preserves the quality of the raisins. Such an apparatus and method is disclosed and claimed herein.